Fuel burner control system



Feb. 15, 1944. 5 ,SSERSTEDT 1 2,341,119

FUEL BURNER CONTROL SYSTEM Filed Nov. 17, 1941 IN VENTOR.

Su ana G. lsszrs'taai I Patented Feb. 15, 1944 FUEL BURNER CONTROL SYSTEM Siegfried G. Isserstedt, Minneapolis, Minn., as-

signor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application November 17, 1941, Serial No. 419,465

9 Claims. (c1. s--2s) The present invention relates generally to a control system for fiuid fuel burners, and is directed more particularly to a system employing automatic starting and stopping means in which the burner will be shut down immediately upon a flame failure at the burner and yet will interpose a substantial standby or scavenger period, before the burner can be automatically started again.

In prior art devices it has been customary to supply combustion responsive devices which take a substantial amount of time, upon the extinguishment of the flame at the burner, to move from their hot to their cold positions. In such instances it is customary to run the starting circuit through the cold contact of the combustion switch so that following a flame failure the burner cannot be restarted until the combustion responsive device closes its cold contact. Such a system is satisfactory where the combustion responsive device moves slowly enough to provide a substantial delay before closing its cold contact.

t is the purpose of the present invention however to'provide a system which is adapted for use with a combustion responsive device which is so sensitive as to be incapable, in and of itself, of providing any substantial delay between the extinguishment of the flame at the burner and the reenergization of the burner motor. l 7 I W One of the main objects of the invention is to provide a fluid fuel burning system having an extremely sensitive combustion responsive device and a separate timer fortiming the scavenger period on recycle. Y

A further object is to provide a system of the above type in which the timer acts to terminate ignition after the combustion responsive device has responded to combustion.

Another object is to provide a systemofthe above type in which the hot and cold combustion switches are not required to overlap in either direction and therefore may be made in the form of a snap switch.

Another object of the invention is to'provide a system in which an extremely sensitive combustion responsive device and timer act; conjointly to shut the system down in the event of aiiame failure and the timer determines the length of the scavenger period on recycle.

These and other objects will readilyfbeco'me apparent to those skilled in the art as the following specification is read in the light of the accompanying drawing which involves a single figure illustrating diagrammatically a fuel burner control system embodying my invention.

Referring. now specifically to the drawing, the reference numeral 10 indicates a sensitive con trol instrument by means of which it is desired to control the fuel burner.

In this instance the control instrument has been shown as comprising a bimetallic element II which is fixed at one end and which carries at its free end a pair of contact blades 12 and 13. The contact blade i2 has been made resilient so that on a decrease in temperature the bimetallic element II will contract and cause the blade I2 first to engage the stationary contact M, and at a slightly lower temperature, cause the blade Hi to make contact with the stationary contact 45.

Indicated generally at I! is an electric timer which has been illustrated as being in the form of a bimetallic blade l8 which is fixed at its lower end and which, when cold, causes its free end to engage the stationary contact l9, and when hot, warps to the left, causing its free end to engage the stationary contact 23. The free end of the bimetallic blade I8 has also been shown as operating any type of snap switch, such as the one indicated generally at 2|. This snap switch has been shown for the purposes of illustration as a common type of overcenter snap switch having a movable arm 22 and an overcenter spring 23. When the timer is in cold po-- sition the snap switch is in the position shown in which the arm 22 is in engagement with the stationary contact 24. When the timer is heated and warps to the left the snap switch will be snapped to its opposite position in which the arm 22 will be in engagement with a stationary stop indicated at 25. An electrical heating element 2B is illustrated adjacent the bimetallic blade l8 for the purpose of causing it to warp from its cold to its hot position.

A combustion responsive switching mechanism has been illustrated diagrammatically as shown at 28, and comprises an arm 29 which engages a cold contact 30 in the absence of combustion and which moves into engagement with the-stationary contact 3! in the presence of combustion. It will be understood that this switching mechanism is not calibrated and therefore does not respond to any set temperature. It merely responds to the presence or absence of combustion at the burner. The hot and cold switches in this switching mechanism do not overlap in either direction; that is, on heating the arm 29 first disengages the contact 30 and then engages the contact 3|, while on cooling the arm first disengages the contact 3| and then engages the contact 30.

Indicated generally at 35 is any usualform of-saf ety switch mechanism in which the contacts are normally latched closed but which may be tripped to open position. by an electrically 'responsive timing means. .In this instance, the switch-is shown as. comprising a pairof resilient contact blades 36 and 37 which are biased apart but which are normally held in closed position by means of the thermallatch 38. As long as this latch is cold, the blades 36 and 3! are'held in closed position, but when heated, for example by the electric heate 39, the blade 38 will warp to the right and release the switch for movement to 3 open position. A trip free manual reset button has been shown at 40. It will be seen that when the button 49 is raised to reset the switch'that the resilient blade 36 will be held out of engage ment with the blade 31 during the time that the switch is being reset, so that it is impossible to manually hold the switch in closed position. I

Indicated generally at 42 is an electromagnetic relay having an actuating winding 43 and a bucking winding 44. That is, when the winding 43 isenergized, the relay pulls in but when the bucking winding 44 is energized while the winding" 43 is energized the effect of the winding" 43 is neutralized andthe relay drops out. This is due to the fact that the winding 44 is wound oppositely to the winding 43 and hence when both windings are energized their magnetic effects cancel each other. The relay 42 is provided with an armature indicated by the dotted line 45, and when the relay is energized the armature pulls in to cause the contact arms 43 and 48toen-' gage the stationary contacts 49 and 5|, respectively. When the relay is deenergized the armature drops out and the arms 43 and 48 move to open contact position either by gravity or by a spring, not shown;

' The system illustrated may be operated to control the usual oil burner which comprises the usual burner motor indicated at 53 and an electric ignition device for igniting the oil shown at 54. It is obvious that this system could be used to control burners employing other types of fuel. The electrical power for operating the system is suppliedby means of the line wires 5% and 51 through a step-down transformer illustrated at 58. The primary winding 59 of this transformer is connected to the line wire 56 by means of conductor 63 and to the line wire ii'lby means of conductor 6!. The transformer 58 is provided with asecondary winding 62.

O t on The parts of the system have been illustrated in the drawing inthe position they will occupy when the room thermostat is satisfied and has been satisfied for a sufficient" length of time to permit the combustion responsive arm 29 to engage its cold contact 38 and to permit the bimetallic timer' is to cool off sufiiciently to'enga'ge its cold contact l9. Under these conditions the ignition control arm 22 will engage its contact 24; but the ignition device will not be energized at' this time due to the fact that the circuit thereto is broken at the contact arm 46 and stationary contact 49/ The secondary winding 62 of the transformer 58 is now disconnected from the system at the roomthermostat and therefore both of the windin s 43'and 44 of the relay 42 are deenergized and the relay is in its out position.

'On a decrease in room temperature the contact arm I2 will first engage the stationary contact l4, but this will close no circuit to the system due to the fact that the contact arm 48 is separated from the contact 5|. Nothing will happen therefore until a further decrease in room temperature causes the contact arm [3 to engage the stationary contact I5. This will establish a circuit from one side of secondary winding 62 through conductor 65, stationary contact I4, switch arms l2 and l3',jcontalct l5, conductor 66, contact l9, timer blade l8; conductor 68, contact 33, switch arm 29, conductors 69 and I0, electricheater 39, conductors 'H and [2, safety switch blades 36 and 31, conductor 13, actuating winding 43 of the relay 42, and conductor 14 back to the other side of the secondary winding 52. i As a result of this circuit the electrical heate'r39'fo'r thesafe'ty' switch will be energized and the relay winding 43 will be energized which will result in the relay armature 45 pulling in and causing the switch blades 46 and 48 to engage their contacts 49 and 51, respectively. Closure of the contact blade 48 with the contact 5| will cause a holding circuit to be set up from one side of the secondary winding 92, through conductor 65, contact l4, switch blade l2, bimetallic element I I, conductor 75, contact 5!, switch arm 48, conductors l6 and iii to the electrical heater 39 and thence through conductors H and 12 to the safety switch and then through the actuating winding 43 and back to the other. side of the secondary 82. It will be noted that this holding circuit is independent both of the bimetallic timer element 18 and the combustion responsive switch arm 29, so. that any movement of these elements at this time, will not drop out they relay.

Engagement of switch arm 46 with stationary, contact 49.wil1 establish three separate. circuits. The first circuit extends. from the line, Wire 55 through conductor 80, contact 49, switch arm 4.6., conductor 8!, burner motor 53, and conduc-v tor 82 back to the other line. Wire. 51. This circuit results in the energization of the burner motor 53 and the resultant delivery of fuel to the burner. Another circuit extends from the line wire 56 through conductor 89, contact 49, switch arm 46, conductors. 83 and, contact arm 22, contact 24, conductor 85, ignition device 54, and conductor 86 back to the line wire 51. This circuit results in the energization of the electrical ignition device 54 for igniting the oil delivered to the burner. A third circuit is established from line wire 56, conductor 80, contact 49, contact arm 45, conductors 83 and 81, electric heating element 23 and conductor 88 a t the in -wire 1- C esure of s ci u n zes he e e tr c h ate 275 w ic at e bimetallic timer I8.

Inasmuch as the burner motor 53 and the elect ical ition de i i are how both eners d omb st on Wil n rm e P od e a d a flame will appear at the burner. The coni: a i n res s ve devi e 3 w i' w un i to move the' contact arm 29 from engagement fromthel col "contact 39: into engagement with the hot contact 3|; This establishes ashunt cir cuit around the heater for the safety switch and the actuating winding 43 of the relay 42 will now be energized by a circuit extending'f'roi'n one side of the secondary winding 62 through conductor 65 contact l4,'contactblade l2, bimetallic element (conductor 15, contact EL'sWitch arm 48,conductors"l6 and G9, switch arm 29, contact 3|, conductors 9 0 and 72 through safety switch 35, conductor 13, actuating winding 43 and conductor '14. back to theother side of the secondary winding 62. Therefore the engagement of the contactarm 29 and the contact 3| effectively deenergizes the heater 39 thereby preventing the unlatching of the safety switch 35, As the bimetallic timer element I 8 heats up and warps into engagement with its hot contact 20, it carries 7 the lower end of the overcenter spring 23 'toward'the left and moves it over center with respect to the contact blade 22 which causes it to disengage its contact 24 and enga e the stop 25. This opens the circuit to the ignition device 54 and this device is therefore deenergized. This is the normal running condition of the system Upon an increase in room temperature, .the bimetallic element II will expand and cause the switch blade to separate from the contact 15. This will not affect the system inasmuch as there is a holding circuit through the contact l4, switchblade l2 and bimetallic element H and down through contact l and switch 48. Upon a furthe increase in room temperature the bimetallic element II will expand further and cause the switch blade l2 to separate from the stationary contact I4. This will break the hold ing circuit to the actuating Winding 43 of the relay 4'2 and the contact arms and 48 will 1 therefore disengage their stationary contacts 49- and 5|. This will result in the deenergization of the burner motor 53 andthe consequent extinguishment of the flame at the burnern As a result, the combustion responsive device 23 will cause the switch arm 29 to disengage contact 3| and reengage the cold contact 30. When a very sensitive combustion responsive device'is used, this action will occur very rapidly. Therefore some other device must be used to prevent the reenergization of the burner before the proper scavenger or standby period has elapsed. This is taken care of by the bimetal timer It. When the switch arm 45 separates from the contact 49 it also deenergizes the electric heater 26 for this bimetallic timer I8. The timer l8 will therefore cool and will, after a predetermined period of time, disengage the hot contact 20 and reengage the cold contact I9, at the same time snapping the switch blade 22 back into engagement with the stationary contact 24. The system is now in condition for a normal start with the parts in the position shown in the drawing. It will be noted, however, that the system can not restart until the bimeta1 timer reengages the cold contact I9, and it is therefore the timer it which determines the scavenger period.

- In the event of a flame failure while thesystem is in running condition the combustion resp'onsive device will react immediately and cause the switch arm 29 to engage the hot contact 3| and engage the cold contact 30. This will establish a circuit from one side of the secondary winding 62 through conductor 65, contact l4, switch blade 12, bimetallic element l I, conductor 15, contact 5|, switch arm 48, conductors l6 and 69, switch arm 29, contact 30, conductor 68, bimetallic blade IB, contact 20, conductor 9|, bucking coil 4 -3, conductors 92 and- '14 back to the other side of the secondary winding 62. It will be seen that this circuit energizes the bucking winding 44 and therefore drops out the relay armature 45, shutting the system down. When the relay armature 45 drops out it deenergizes the heater 26 for the bimetallic timer l8 and after a predetermined period of time this timer tact 30 with the result that the electric heater 39 for the safety switch will remainenergized, and after a predetermined period of time will release the safety switch blade 36 which will then move to open circuit position. This breaks the circuit to the actuating winding 43 forthe relay 42 and the armature 45 will drop out and the system will be shut down. The system cannot now be restarted until the manual push button 40 is operated to reset the safety switch to closed position. This will not be done of course until the difficulty which prevented the establishment of combustion at the burner has been remedied.

It will therefore be seen that I have designed an intermittent ignition oil burner control system which will shut down immediately upon the failure of flame at the burner and which will recycle after a predetermined scavenger period has elapsed. It should also be noted that even though a very sensitive combustion responsive device may be used which will operate substantially immediately upon the appearance and disappearance of flame at the burner, the system cannot immediately reenergize the burner motor after it has been shut down because a timer is used to interpose a predetermined minimum time delay between successive burner energizations.

It will also be seen that I have eliminated the necessity for utilizing a combustion responsive device in which the hot and cold switches must overlap either on heating or cooling.

As many changes and modifications of this invention will undoubtedly occur to those who are skilled in the art, I wish it to be understood that I intend to be limited only by the scope ofthe appended claims.

I claim as my invention:

1. A fluid fuel burner control system comprising in combination, a burner, an electrical device for supplying fuel to the burner, a combustion responsive device having-a cold switch, an electrically operated timer having a first switch which is closed when said timer is deenergized and a second switch which is closed when said timer is energized, a main switch, a first circuit including said main switch, first switch and cold switch, relay means energized as a result of closure of said circuit for rendering said electrical device operative to supply fuel and for energizing said timer, said relay means closing a holding circuit for itself independent of said timer and combustion switches, and means including said second switch and said cold switch for rendering said electrical device inoperative.

2. A fluid fuel burner control system comprising in combination, an electrical device for supplying fuel to said burner, a, combustion responsive device having hot and cold switches, a timer closing a first switch when deenergized and a second switch when energized, a main switch, a

relay, a normally closed safety switch in control of said electrical device, electrical time delay means for opening said safety switch, an energizing circuit for said relay including said main switch, first switch, cold switch, and electrical time delay means, said relay, when energized, closing a holding circuit for itself which is independent of said first switch and cold switch, and also energizing said timer and rendering said electrical device operative to supply fuel to the burner, means for deenergizing said electrical time delay means including said hot switch, and

switch arm 29 in engagement'with the cold con-' means for deenergizing said relay including said cold switch and second. switch.

3, A fluid fuel burner control system comprising in combination, a burner, an electrical device for supplying fuel to the burner, a combustion responsive device having a, cold switch, an electrically operated timer having a firstv switch which is closed when said timer is deenergized and a second switch which is closed when said timer is, energized, a main switch, a relay having an actuating winding and a bucking. winding, a first circuit including said main switch, first. switch, cold switch, and actuating Winding, a holding circuit closed by said relay independent of said first switch and cold switch, said relay rendering said electrical device operative to supply fuel and also energizing said timer, and a circuit for said bucking winding including said second switch and cold switch.

4. A fluid fuel burner control system comprising in combination, an electrical device for supplying fuel to said burner, a combustion responsive device having hot and cold switches, a timer closing a first switch when deenergized and a second switch when energized, a main switch, a relay, a normally closed safety switch in control of said electrical device, electrical time delay means for opening said safety switch, an actuating winding and a bucking winding for said relay, a first circuit including said main switch, first switch, cold switch, and electrical time delay means, a holding circuit closedby said relay independent of said first switch and cold switch, said relay energizing said timer and rendering said electrical device operative to supply fuel to the burner, means for deenergizing, said electrical time delay means including said hot. switch, and a circuit for said bucking winding including said cold switch and second switch.

5. A fluid fuel burner control system comprising in combination, a burner, an electrical device for supplying fuel tothe burner, an ignition device for said fuel, an ignition switch, a combustion responsive device having a cold switch, an electrically operated timer having a first switch which is closed when said timer is deenergized and a second switch which is closed when, said timer is energized, a main switch, a first circuit including said main switch, first switch and cold switch, relay means energized as a result of closure of said circuit for rendering said electrical device operative to supply fuel, for rendering said ignition device operative to ignite said fuel, and for energizing said timer, said timer subsequently opening said ignition switch to terminate. igniton, said relay means closing a holding circuit for itself independent of said timer and combustion switches, and means including said second switch and said cold switch for rendering said electrical device inoperative.

6. A fluid fuel burner control system'comprising in combination, an electrical device for supplying fuel to said burner, an ignition device for igniting said fuel, an ignition switch, a combustion, responsive device having hot and cold switches, a timer closing a first switch when deenergized and a second switch when energized, a main switch, a relay, a normally closed safety switch in control of said electrical device, electrical time delay means for opening said safety switch, an energizing circuit for said relay including said main switch, first: switch, cold switch, and electrical time delay means, said relay, when energized, closing av holding circuitv for itself which is, independent. of. saidfirst switch and cold switch, and also energizing said timer, rendering said electrical device operative to supply fuel to the burner, and rendering said ignition device operative. to ignite said fuel, means for deenergizing said electrical time delay means including said hot switch, said timer operating-as a result of its energization to open said ignition switch, and means for deenergizing said relay including said cold switch and second switch.

7. A fluid fuel burner. control system comprising. in combination, a burner, an. electrical device for supplying fuel to said burner, a, combustion responsive device having. a hot switch and a. cold switch, a timer switch, a timer for closing said timer switch when deenergized and opening said timer switch when energized, a main switch, a relay, a normally closed. safety switch in control of said electrical device, electrical time delay means for opening said safety switch, an; energizing circuit. for said. relay controlled by said main switch, timer switch, and electrical time delay means, said relay, when energized, closing a holding. circuit for itself which is independent of said timer switch, and also energizing said;

timer and rendering said electricalv device oper-.

ative to supply fuel to theburner, means including said hot switch for deenergizing said. electrical time delay means, and means including said cold switch, and said timing device for de-. energizing said relay for a timed period upon. combustion failure.

8., A fluid fuel: burner control system comprising in combination, a. burner, an electrical device for supplying fuel to said burner, an ignition, device for said fuel, an ignition switch, av combustion responsive device having a hot switch and a. cold, switch, a timer switch, a timer for closing said timer switch when, deenergized and opening said, timer switch, when energized, a main switch, av relay, a normally closed; safety switch in control of said electrical device, electrical time. delay means for opening said safety switch, an energizing circuit for. said relay controlled. by saidmain switch, timer switch, and electrical time deignitlOncircuit after a predetermined periodlofn time, means including said not switch for deenergizing said electrical time delay means, and.

means including said cold switch and said timing device for deenergizing said relay for a timed, period, upon combustion failure.

9. In burner control mechanism for an electrical device. for controling the supply of fuel to aburner, a combustion responsive device having a. cold, switch, an electrically operated timer hav.

ing a first switch which is closed when said, timer is deenergized' and a'second' switch which is closed when said timer is, energized, means for establishing a. first circuit including said first:

switch, said cold switch, and a main switch, re'-,

lay means energized as a result, of closure of. said circuit and adapted to render said electrical, device operative to-supply fuelandfor energizing said timer,,said. relay means being adapted: to close a holding, circuit for'itself independent.

ofsaid timer andcombustion switchesand means:

including said second switchand said cold switclr,

for causing; deenergizationof, saidrelay. I

SIEGFRIED G; ISSERSIIEDE. 

